Motor-vehicle electronic control units in particular for electronic or electro-hydraulic braking systems are known per se to comprise at least one microcontroller system consisting of a single-core or multicore microcontroller unit (MCU) and a single-core or multicore mixed-signal integrated circuit (mixed-signal IC) as a power control unit (PCU). The MCU is used in particular for performing the computations needed to operate the motor vehicle system, while the PCU is provided, for example, for driving power transistors in order to provide open-loop and closed-loop control of the motor vehicle system. MCU and PCU here communicate with each other via what is known, as a de facto standard, as a serial peripheral interface (SPI). The SPI works in duplex mode using five signal lines:                SIMO—data signal: Slave In, Master Out;        SOMI—data signal: Slave Out, Master In;        SCK—clock signal output by the master; and        two slave-select lines, which the master uses to specify the node, or slave, with which it wishes to communicate.        
According to the configuration described here, the MCU is the master, which provides the clock signal. While the MCU is transmitting data to the PCU on the SIMO line, the PCU is simultaneously transmitting data to the MCU on the SOMI line. A half clock-signal period of the clock signal (SCK) is available for this circular communication. These SPI implementations provide prioritizable local data memories in the MCU, which allow SPI communication to be scheduled and executed efficiently in terms of transfer time. Polling-based control is used solely for transfers that cannot be scheduled. Such known MCU/PCU configurations thereby achieve transfer rates of the order of 8 to 11 MBd (megabaud) for example.
The limitation on the transfer rates of these known systems arises from the time constraints of the circular communication of the SPI interface, which is defined by the propagation of the clock signal from the master to the slave, and from the performance of the technology, in particular of the digital components of the PCU. The fabrication process for the PCU provides analog power transistors, analog transistors and digital transistors, and therefore cannot be optimized for the production of digital transistors. This means that the maximum achievable clock frequency is slower by a factor of 4 to 5 compared with the MCU, which can be optimized in this respect. Whereas the clock frequency of the MCU equals 120 to 160 MHz, for instance, only 20 to 40 MHz can hence be achieved by the internal clock of the PCU.